The interaction of GnRH with anterior pituitary tissue obtained from sheep and rats is being investigated. The effects of steriod hormones on the number, affinity and sub-cellular distribution of receptors for GnRH in pituitary tissue are being determined by Scatchard plot analysis and by quantitive electron microscopic autoradiography. The affinities of the GnRH receptor for a series of agonists and antagonists of GnRH is being studied to determine if the biopotency of the analogs are correlated to the affinity of their interaction with receptor.